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通过扩展改善ASP.NET MVC的验证机制[实现篇]

原文:通过扩展改善ASP.NET MVC的验证机制[实现篇]

在《使用篇》中我们谈到扩展的验证编程方式,并且演示了本解决方案的三大特性:消息提供机制的分离多语言的支持多验证规则的支持,我们现在来看看这样的验证解决方案最终是如何实现的。

目录:
一、为验证创建一个上下文:ValidatorContext
二、通过自定义ActionInvoker在进行操作执行之前初始化上下文
三、为Validator创建基类:ValidatorBaseAttribute
四、通过自定义ModelValidatorProvider在验证之前将不匹配Validator移除
五、RequiredValidatorAttribute的定义

一、为验证创建一个上下文:ValidatorContext

“基于某个规则的验证”是本解决方案一个最大的卖点。为了保持以验证规则名称为核心的上下文信息,我定义了如下一个ValidatorContext(我们本打算将其命名为ValidationContext,无奈这个类型已经存在)。ValidatorContext的属性RuleName和Culture表示当前的验证规则和语言文化(默认值为当前线程的CurrentUICulture),而字典类型的属性Properties用户存放一些额外信息。当前ValidationContext的获取与设置通过静态Current完成。

   1: public class ValidatorContext
   2: {
   3:     [ThreadStatic]
   4:     private static ValidatorContext current;
   5:  
   6:     public string RuleName { get; private set; }
   7:     public CultureInfo Culture { get; private set; }
   8:     public IDictionary<string, object> Properties { get; private set; }
   9:  
  10:     public ValidatorContext(string ruleName, CultureInfo culture=null)
  11:     {
  12:         this.RuleName = ruleName;
  13:         this.Properties = new Dictionary<string, object>();
  14:         this.Culture = culture??CultureInfo.CurrentUICulture;
  15:     }
  16:  
  17:     public static ValidatorContext Current
  18:     {
  19:         get { return current; }
  20:         set { current = value; }
  21:     }
  22: }

我们为ValidatorContext定义了如下一个匹配的ValidatorContextScope对象用于设置ValidatorContext的作用范围。

   1: public class ValidatorContextScope : IDisposable
   2: {
   3:     private ValidatorContext current = ValidatorContext.Current;
   4:     public ValidatorContextScope(string ruleName, CultureInfo culture = null)
   5:     {
   6:         ValidatorContext.Current = new ValidatorContext(ruleName, culture);
   7:     }
   8:     public void Dispose()
   9:     {
  10:         if (null == current)
  11:         {
  12:             foreach (object property in ValidatorContext.Current.Properties.Values)
  13:             {
  14:                 IDisposable disposable = property as IDisposable;
  15:                 if (null != disposable)
  16:                 {
  17:                     disposable.Dispose();
  18:                 }
  19:             }
  20:         }
  21:         ValidatorContext.Current = current;
  22:     }
  23: }

二、通过自定义ActionInvoker在进行操作执行之前初始化上下文

通过《使用篇》中我们知道当前的验证规则名称是通过ValidationRuleAttribute来设置的,该特性不仅仅可以应用在Action方法上,也可以应用在Controller类型上。当然Action方法上的ValidationRuleAttribute具有更高的优先级。如下面的代码片断所示,ValidationRuleAttribute就是一个包含Name属性的普通Attribute而已。

   1: [AttributeUsage( AttributeTargets.Class| AttributeTargets.Method)]
   2: public class ValidationRuleAttribute:Attribute
   3: {
   4:     public string Name { get; private set; }
   5:     public ValidationRuleAttribute(string name)
   6:     {
   7:         this.Name = name;
   8:     }
   9: }

很显然,以当前验证规则验证规则为核心的ValidatorContext需要在Action操作之前设置(严格地说应该在进行Model绑定之前),而在Action操作完成后清除。很自然地,我们可以通过自定义ActionInvoker来完成,为此我定义了如下一个直接继承自ControllerActionInvoker的ExtendedControllerActionInvoker类。

   1: public class ExtendedControllerActionInvoker : ControllerActionInvoker
   2: {
   3:     public ExtendedControllerActionInvoker()
   4:     { 
   5:         this.CurrentCultureAccessor= (context=>
   6:             {
   7:                 string culture = context.RouteData.GetRequiredString("culture");
   8:                 if(string.IsNullOrEmpty(culture))
   9:                 {
  10:                     return null;
  11:                 }
  12:                 else
  13:                 {
  14:                     return new CultureInfo(culture);
  15:                 }
  16:             });
  17:     }
  18:     public virtual Func<ControllerContext, CultureInfo> CurrentCultureAccessor { get; set; }
  19:     public override bool InvokeAction(ControllerContext controllerContext, string actionName)
  20:     {
  21:         CultureInfo originalCulture = CultureInfo.CurrentCulture;
  22:         CultureInfo originalUICulture = CultureInfo.CurrentUICulture;
  23:         try
  24:         {
  25:             CultureInfo culture = this.CurrentCultureAccessor(controllerContext);
  26:             if (null != culture)
  27:             {
  28:                 Thread.CurrentThread.CurrentCulture = culture;
  29:                 Thread.CurrentThread.CurrentUICulture = culture;
  30:             }
  31:             var controllerDescriptor = this.GetControllerDescriptor(controllerContext);
  32:             var actionDescriptor = this.FindAction(controllerContext, controllerDescriptor, actionName);
  33:             ValidationRuleAttribute attribute = actionDescriptor.GetCustomAttributes(true).OfType<ValidationRuleAttribute>().FirstOrDefault() as ValidationRuleAttribute;
  34:             if (null == attribute)
  35:             {
  36:                 attribute = controllerDescriptor.GetCustomAttributes(true).OfType<ValidationRuleAttribute>().FirstOrDefault() as ValidationRuleAttribute;
  37:             }
  38:             string ruleName = (null == attribute) ? string.Empty : attribute.Name;
  39:             using (ValidatorContextScope contextScope = new ValidatorContextScope(ruleName))
  40:             {
  41:                 return base.InvokeAction(controllerContext, actionName);
  42:             }
  43:         }
  44:         catch
  45:         {
  46:             throw;
  47:         }
  48:         finally
  49:         {
  50:             Thread.CurrentThread.CurrentCulture = originalCulture;
  51:             Thread.CurrentThread.CurrentUICulture = originalUICulture;
  52:         }
  53:     }
  54: }

如上面的代码片断所示,在重写的InvokeAction方法中我们通过ControllerDescriptor/ActionDescriptor得到应用在Controller类型/Action方法上的ValidationRuleAttribute特性,并或者到设置的验证规则名称。然后我们创建ValidatorContextScope对象,而针对基类InvokeAction方法的执行就在该ValidatorContextScope中执行的。初次之外,我们还对当前线程的Culture进行了相应地设置,默认的Culture 信息来源于当前RouteData。

为了更方便地使用ExtendedControllerActionInvoker,我们定义了一个抽象的Controller基类:BaseController。BaseController是Controller的子类,在构造函数中我们将ActionInvoker属性设置成我们自定义的ExtendedControllerActionInvoker对象。

   1: public abstract class BaseController: Controller
   2: {
   3:     public BaseController()
   4:     {
   5:         this.ActionInvoker = new ExtendedControllerActionInvoker();
   6:     }
   7: }

三、为Validator创建基类:ValidatorBaseAttribute

接下来我们才来看看真正用于验证的验证特性如何定义。我们的验证特性都直接或者间接地继承自具有如下定义的ValidatorBaseAttribute,而它使ValidationAttribute的子类。如下面的代码片断所示,ValidatorBaseAttribute还实现了IClientValidatable接口,以提供对客户端验证的支持。属性RuleName、MessageCategory、MessageId和Culture分别代表验证规则名称、错误消息的类别和ID号(通过这两个属性通过MessageManager这个独立的组件获取完整的错误消息)和基于的语言文化。

   1: [AttributeUsage(AttributeTargets.Class|AttributeTargets.Field | AttributeTargets.Property, AllowMultiple = false)]
   2: public abstract class ValidatorBaseAttribute : ValidationAttribute, IClientValidatable
   3: {
   4:     
   5:     public string RuleName { get; set; }
   6:     public string MessageCategory { get; private set; }
   7:     public string MessageId { get; private set; }
   8:     public string Culture { get; set; }
   9:  
  10:     public ValidatorBaseAttribute(MessageManager messageManager, string messageCategory, string messageId, params object[] args)
  11:         : base(() => messageManager.FormatMessage(messageCategory, messageId, args))
  12:     {
  13:         this.MessageCategory = messageCategory;
  14:         this.MessageId = messageId;
  15:     }
  16:  
  17:     public ValidatorBaseAttribute(string messageCategory, string messageId, params object[] args)
  18:         : this(MessageManagerFactory.GetMessageManager(), messageCategory, messageId, args)
  19:     { }
  20:  
  21:     public virtual bool Match(ValidatorContext context, IEnumerable<ValidatorBaseAttribute> validators)
  22:     {
  23:         if (!string.IsNullOrEmpty(this.RuleName))
  24:         {
  25:             if (this.RuleName != context.RuleName)
  26:             {
  27:                 return false;
  28:             }
  29:         }
  30:  
  31:         if (!string.IsNullOrEmpty(this.Culture))
  32:         {                
  33:             if (string.Compare(this.Culture, context.Culture.Name, true) != 0)
  34:             {
  35:                 return false;
  36:             }
  37:         }
  38:  
  39:         if (string.IsNullOrEmpty(this.Culture))
  40:         {
  41:             if (validators.Any(validator => validator.GetType() == this.GetType() && string.Compare(validator.Culture, context.Culture.Name, true) == 0))
  42:             {
  43:                 return false;
  44:             }
  45:         }
  46:         return true;
  47:     }
  48:     public abstract IEnumerable<ModelClientValidationRule> GetClientValidationRules(ModelMetadata metadata, ControllerContext context);
  49:     private object typeId;
  50:     public override object TypeId
  51:     {
  52:         get { return (null == typeId) ? (typeId = new object()) : typeId; }
  53:     }
  54: }

由于我们需要将多个相同类型的Validator特性应用到某个类型或者字段/属性上,我们需要通过AttributeUsageAttribute将AllowMultiple属性设置为True,此外需要重写TypeId属性。至于为什么需需要这么做,可以参考我的上一篇文章《在ASP.NET MVC中如何应用多个相同类型的ValidationAttribute?》。对于应用在同一个目标元素的多个相同类型的Validator特性,只有与当前ValidatorContext相匹配的才能执行,我们通过Match方法来进行匹配性的判断,具体的逻辑是这样的:

  • 在显式设置了RuleName属性情况下,如果不等于当前验证规则,直接返回False;
  • 在显式设置了Culture属性情况下,如果与当前语言文化不一致,直接返回False;
  • 在没有设置Culture属性(语言文化中性)情况下,如果存在另一个同类型的Validator与当前的语言文化一致,也返回False;
  • 其余情况返回True

四、通过自定义ModelValidatorProvider在验证之前将不匹配Validator移除

应用在Model类型或其属性/字段上的ValidationAttribute最终通过对应的ModelValidatorProvider(DataAnnotationsModelValidatorProvider)用于创建ModelValidator(DataAnnotationsModelValidator)。我们必须在ModelValidator创建之前将不匹配的Validator特性移除,才能确保只有与当前ValidatorContext相匹配的Validator特性参与验证。为此我们通过继承DataAnnotationsModelValidator自定义了如下一个ExtendedDataAnnotationsModelValidator。

   1: public class ExtendedDataAnnotationsModelValidatorProvider : DataAnnotationsModelValidatorProvider
   2: {
   3:     protected override IEnumerable<ModelValidator> GetValidators(ModelMetadata metadata, ControllerContext context, IEnumerable<Attribute> attributes)
   4:     {
   5:         var validators = attributes.OfType<ValidatorBaseAttribute>();
   6:         var allAttributes = attributes.Except(validators).ToList();
   7:         foreach (ValidatorBaseAttribute validator in validators)
   8:         {
   9:             if (validator.Match(ValidatorContext.Current, validators))
  10:             {
  11:                 allAttributes.Add(validator);
  12:             }
  13:         }
  14:         return base.GetValidators(metadata, context, allAttributes);
  15:     }
  16: }

如上面的代码片断所示,在重写的GetClientValidationRules方法中,输入参数attributes表示所有的ValidationAttribute,在这里我们根据调用ValidatorBaseAttribute的Match方法将不匹配的Validator特性移除,然后根据余下的ValidationAttribute列表调用基类GetValidators方法创建ModelValidator列表。值得一提的是,关于System.Attribute的Equals/GetHashCode方法的问题就从这个方法中发现的(详情参见《为什么System.Attribute的GetHashCode方法需要如此设计?》)。自定义ExtendedDataAnnotationsModelValidator在Global.asax的Application_Start方法中通过如下的方式进行注册。

   1: protected void Application_Start()
   2: {
   3:      //...
   4:     var provider = ModelValidatorProviders.Providers.OfType<DataAnnotationsModelValidatorProvider>().FirstOrDefault();
   5:     if (null != provider)
   6:     {
   7:         ModelValidatorProviders.Providers.Remove(provider);
   8:     }
   9:     ModelValidatorProviders.Providers.Add(new ExtendedDataAnnotationsModelValidatorProvider());
  10: }

五、RequiredValidatorAttribute的定义

最后我们来看看用于验证必需字段的RequiredValidatorAttribute如何定义。IsValid用于服务端验证,而GetClientValidationRules生成调用客户端验证规则。

   1: [AttributeUsage(AttributeTargets.Field | AttributeTargets.Property, AllowMultiple = true)]
   2: public class RequiredValidatorAttribute : ValidatorBaseAttribute
   3: {
   4:     public RequiredValidatorAttribute(string messageCategory, string messageId, params object[] args)
   5:         : base(messageCategory, messageId, args)
   6:     { }   
   7:  
   8:     public override bool IsValid(object value)
   9:     {
  10:         if (value == null)
  11:         {
  12:             return false;
  13:         }
  14:         string str = value as string;
  15:         if (str != null)
  16:         {
  17:             return (str.Trim().Length != 0);
  18:         }
  19:         return true;
  20:     }
  21:  
  22:     public override IEnumerable<ModelClientValidationRule> GetClientValidationRules(ModelMetadata metadata, ControllerContext context)
  23:     {
  24:         return new ModelClientValidationRequiredRule[] { new ModelClientValidationRequiredRule(this.ErrorMessageString) };
  25:     }
  26: }